Military vehicles must be able to operate effectively an the battlefield when under attack or threat of attack by nuclear, biological and chemical (NBC) weapons. To ensure that crew efficiency is maintained, collective protection is normally provided by creating a clean environment within the closed down vehicle crew space with filtered air. Under such conditions the crew can continue to operate without the encumbrance of protective gloves and respirators which greatly reduce crew operating effectiveness. Nonetheless, NBC suits would normally be worn-at all times due to the difficulty of donning them within the confined space of the vehicle.
For the vehicle to remain habitable and for the crew to operate as an efficient military unit, an efficient cooling system is necessary to meet the physiological requirements for vehicle habitation in a closed down vehicle with the crew wearing NBC protective suits. Systems providing collective NBC protection and cooling or heating of the crew cabin environment are referred to as "environmental life support systems".
Traditionally, environmental life support systems for military vehicles have been based upon activated charcoal filters, cooling being by vapour cycle refrigeration. Although providing a high level of-protection, activated charcoal filters are not regenerative and must be discarded and replaced following a chemical attack. The effective life of the filters is dependent on the concentration and nature of the challenge but may only be a few hours with some NBC agents.
This severely limits the effective operation of a vehicle on a battlefield when NBC weapons are deployed against them and creates high operational costs due to the logistics chain required to provide a regular supply of new filters to forward areas of the battlefield to support the vehicle fleet, and also the concomitant removal and disposal of contaminated filters. More recently systems have been developed based upon regenerative filtration in place of the non-reusable activated carbon elements.
The energy requirements for environmental life support systems has been a constraint on their adoption and deployment.
A number of proposals have been made to provide systems utilizing pressure swing adsorbtion (PSA) systems developed by PALL Corporation.
Pressure swing adsorbtion systems use filter beds filled with a sorbent material which adsorbs gases under pressure and desorbs gases once the pressure is removed. The system has two filter beds, one on stream and fed with contaminated air under pressure from which gases are removed. At the same time, the other off stream bed is regenerating and being purged with depressurised filtered air. On completion of the cycle, the role of each bed is reversed, the operation being controlled by an automatic sequence timer to provide continuous uninterrupted service. Industrial PSA systems have been shown to operate for many years without degradation of performance or air quality. PSA systems developed by PALL Corporation have been shown to be efficient in removing all known chemical agents. To demonstrate the suitability of PALL Corporation's PSA systems, a six month test was provided by the TNO Prins Maurits Laboratory in The Netherlands in 1988 testing a PSA using both simulants and live agents. The unit was challenged by a threat scenario developed in coordination with TNO and with the US Army's Edgewood Research Development and Engineering Centre and included nerve, blood and blister agents as well as a carbon breaker unit. The unit removed all the chemical agents to below the detection-limits of the instrumentation and proved conclusively that PSA technology was a viable concept for NBC collective protection systems. Further tests were carried out by Battelle Memorial Institute in 1991 at the behest of the US Air Force testing a full scale pressure swing adsorber.
A number of proposals for environmental life support systems using PSA have appeared, as, a consequence, in the patent literature.
U.S. Pat. No. 4,732,579, Veltman et al assigned to FMC Corporation, proposes a system and method for providing a continuous supply of clean air at a desired temperature to the crew members of a combat vehicle. The contaminated air is said to be initially compressed by energy received from the exhaust gases from a combustion power unit of the vehicle, the initially compressed air being cooled to increase its density and then compressed and cooled a second time before being passed through a pressure swing adsorbent system. Air from the PSA system is expanded and changed in temperature to provide clean air to personnel within the vehicle. Energy released from the air during expansion is used to compress the air in the secondary compressor. The off line PSA bed is purged with clean air from the an line bed which is expanded through an orifice to lower its pressure.
U.S. Pat. No. 4,769,051, Defranceso assigned to United Technologies Corporation, discloses an air conditioning system powered by a supply of compressed air. The compressed air passes to an air cycle machine having a compressor, a turbine and a load heat exchanger. Air from the compressor is communicated to the turbine which expands and cools the air before passing it to the load heat exchanger. A PSA system cleans air as it passes from the compressor to the turbine before expansion. Purge air for the PSA system is derived from the clean air exiting the load heat exchanger after first passing it through a regenerative heat exchanger which abstracts heat from the air as it passes from the compressor to the PSA system before passing on to the turbine.
U.S. Pat. No. 5,213,593, White et al assigned to PALL Corporation, proposes a PSA system which has first and second sorbing chambers, each of which includes first and second openings defining a gas flow path between them and a sorbent bed disposed in the gas flow path and having a sorption inlet region near the first opening, and a heater positioned near the sorption inlet region. The heaters are operated from an external energy source. A valve arrangement interconnects an intake, an exhaust and the first openings of the first and second sorbing chambers and interconnects an outlet with the second openings of the first and second sorbing chambers. Gas is directed through one sorbing chamber to the outlet. At the same time a portion of the outlet gas is directed through the other sorbing chamber to the exhaust. Energy from the external energy source is coupled to the heater of the other sorbing chamber to heat the sorption inlet region of the other sorbing chamber as the outlet gas flows through the sorption inlet region. The controller is adapted to cycle between the first and second sorbing chambers according to a NEMA cycle length of less than about five minutes. One sorbent bed sorbs at least a portion of contaminant from the gas and is heated by the heat of adsorption and the other sorbent bed is regenerated using both the energy supplied by the heater and the heat of adsorption.